A STELLAR SPECTRAL FLUX LIBRARY BY A.J. PICKLES (1998) (PASP 110, 863)

This library of wide spectral coverage, consists of 131 flux calibrated stellar spectra, encompassing all normal spectral types and luminosity classes at solar abundance, and metal-weak and metal-rich F-K dwarf and G-K giant components. Each spectrum in the library is a combination of several sources overlapping in wavelength coverage. The creator of the library has followed precise criteria to combine sources and to assemble the most reliable spectra. As part of the selection criteria prior to combination, all input sources were checked aginst the SIMBAD database and against the colors and line strengths as derived by the observed spectra themselves to make sure they had similar spectral types.

In the following, the list of the above mentioned input sources is given, numbered following Table 1 in the original paper.

1. Sviderskiene (1988)
2. Heck et al. (1984)
3. Gunn and Stryker (1983)
4. Kiehling (1987)
5. Jacobi, Hunter and Christian (1984)
6. Silva and Cornell (1992)
7. Pickles (1985)
8. Pickles and van der Kruit (1990)
9. Serote Roos, Boisson and Joly (1996)
10. Danks and Dennefeld (1994)
11. Lancon and Rocca-Volmerange (1992)
12. Dallier, Boisson and Joly (1996)
13. Kleinmann and Hall (1986)
14. Cohen et al. (1995, 1996a, 1996b)
15. Fluks et al. (1994)

Table 1 of Pickles (1998) precisely identifies what of the above sources entered the combination to create the complete set of spectral types. The output wavelength grid was chosen to be 1150-25000 Angstrom, with a sampling interval of 5 Angstrom per pixel and resolution of ~500 Angstrom. In the end, two separate libraries were created, UVILIB and UVKLIB, that cover the spectral range 1150-10620 Angstrom, and 1150-25000 Angstrom, respectively. In fact, only half of all spectral types in the library (mainly later types of solar abundance) have longer spectral coverages available.

The following quick-look table gives an idea of the spectra available. Spectra are ordered by progressive number, according to the spectral type (decreasing effective temperature) and luminosity class. The same ordering sequence is valid for both the UVILIB and the UVKLIB libraries, where the suffix "uk" differentiates between two spectra of the same spectral type but with different wavelength coverage (see ahead the section on the CDBS/HST Pickles library).

Table 1: Pickles library spectra:

Some reasons why it is worth to use this library may be summarized as follows:

1. it provides an uniform and complete flux library of observed spectra representing normal stellar types, and
2. each spectrum was put together after selecting the best spectra in each wavelength interval, grouping them by spectral type, luminosity class and abundance (and color and line strength), to produce a final product with an uniform grid.

THE HST/CDBS VERSION OF THE PICKLES LIBRARY

The library installed in CDBS and distributed within STSDAS is from here. This library is divided in 2 independent subdirectories, according to spectral coverage, and exactly reproducing the structure of the original library by Pickles. Subdirectory dat_uvi groups all spectra derived from all ultraviolet, optical and near infrared sources, in the wavelength range 1150-10620 Angstrom. This library has complete spectral coverage for all components over this wavelength range, and is (in the original library) referred to as UVILIB. Subdirectory dat_uvk groups all spectra that were derived by combining the UVILIB spectra with additional infrared data to a long wavelength limit of 25000 Angstrom. This is originally referred to as UVKLIB. Within each subdirectory each spectrum is given in STSDAS table format: the first column gives the wavelength for the given spectral range, and the second column gives the flux. Fluxes are tabulated in units of erg/s/cm^2/A and were calculated by normalizing the original fluxes in the Pickles V band to a 0 magnitude in vegamag. In the vegamag system, Vega has magnitude zero in all passbands.

For the UVILIB spectra, the names of the files are given as pickles_ttt.fits where "pickles", for Pickles, is the library identifier and "ttt" is a number ranging from 1 to 131. For the UVKLIB spectra, the names have the format pickles_uk_ttt.fits, following the same nomenclature, and with the suffix "uk" provided as to distinguish them from the shorter wavelength library.

The complete list of stars of different spectral type and luminosity class together with the corresponding Pickles file is presented in Table 2. The effective temperature information is extracted from Table 2 of Pickles (1998). A "w" or an "r" preceding the spectral type indicates a "weak" or "rich" metallicity in respect to solar.

Table 2: Spectral type and Effective temperature corresponding to the Pickles spectra in the library.

A similar list applies for the UKVKLIB library. For these spectra the names have the format "pickles_uk_ttt.fits". A reduced form of Table 2 can also be found in the library installed in CDBS and is named pickles.fits for the spectra in dat_uvi, and pickles_uk.fits for the spectra in dat_uvk directory. A "w" or an "r" preceding the spectral type indicates a "weak" or "rich" metallicity in respect to solar.

USE OF THE PICKLES STAR SPECTRA WITH SYNPHOT

Use of these spectra should be exactly similar to other libraries already available in synphot. The desired spectrum is provided in input in any of the synphot tasks as appropriate with no particular syntax. For examples on how to use spectra from the synphot atlas library, please refer to the Synphot Data User's Guide.